There should be a shutoff valve in the intake (where a throttle body would be on a gas engine) that shuts off the flow of air to the engine, shutting it off. This system will prevent "runaway diesel if you have blowby in the rings, otherwise the car will suck oil past the rings and keep running on that, even if it has no fuel. The only sure way to shut off a diesel is by eliminating the source of air, in an emergency you can put a solid object across the intake.